Apparatus and method of power control

ABSTRACT

The present disclosure is related to a power control apparatus and a method for controlling power, more specifically to a power control apparatus that controls the risk of overcurrent in a power generator when the voltage in the power grid is low. In accordance with an embodiment of the present disclosure, a power control apparatus that controls power in a power generation system including a generator generating power can include a current comparator, which calculates an error current by using a difference between a current measured at the generator and a rated current of the generator, a controlling unit, which calculates a real power value by receiving the error current and outputs a switch driving signal corresponding to the calculated real power value, a switch, which is operated by the switch driving signal, and a resistance device, which is coupled to the switch to consume the error current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/424,418, which claims the benefit of priority under 35 U.S.C§§120,365, and 371 to Patent Cooperation Treaty Patent Application No.PCT/KR2009/001697, filed on Apr. 2, 2009, which claims the benefit ofKorean Application Nos. 10-2008-0050696, filed May 30, 2008, and10-2008-0102083, filed Oct. 17, 2008. The disclosures of the aboveapplications are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure is related to a power control apparatus and amethod for controlling power, more specifically to a power controlapparatus that controls the risk of overcurrent in a power generatorwhen the voltage in the power grid is low.

DISCUSSION OF THE RELATED ART

Generally, electric power systems, such as power generation systems andpower transmission systems, have some protection device or mechanism tocontrol the risk of overcurrent and overvoltage in order to maintain astable power grid.

In the conventional technology, an electric power system uses a 3-phaseAC/CD/AC pulse-width modulation (PWM) converter for its power converter.A converter, which is connected to AC power, an inverter, which isconnected to the load, and a DC capacitor, which serves as a bufferbetween the converter and the inverter, have been connected to suchpower converter. An electrolytic capacitor has been commonly used forthe DC capacitor, especially as a filter or an energy buffer because ofthe large capacity compared to its relatively low cost.

The capacitor may produce heat due to electric currents, reducing thecapacitance and shortening the lifetime of the capacitor. Thus, it isrequired that the capacitance of the capacitor be precisely measured orestimated in the electric power system including a DC capacitor, inorder to diagnose the lifetime of the capacitor and anticipate thereplacement time of the capacitor.

However, in order to measure the capacitance, it is required that thecapacitor be separated from the system.

Furthermore, even though the capacitance may be estimated relativelyaccurately through a number of experimental results and algorithms,without separating the capacitor from the system, the electric powersystem does not come equipped with a device that can control power so asto prevent the power generation system from being separated from thepower grid when an accident occurs during the system operation.

In the conventional technology, the electric power system includes apower control apparatus encompassing a DC-DC converter, which converts asource of direct current (DC) from one voltage level to another. Here,the power control apparatus includes the DC-DC converter inside thepower converter, and may be placed between the converter and theinverter. Therefore, the DC-DC converter may control power by limitingthe direct current between the converter and the inverter, or convertingthe direct current into DC voltage.

However, the conventional electric power system is not capable ofcontrolling the power by detecting the change in electric current inreal time to prevent the power generation system from being separatedfrom the power grid when an accident occurs during the system operation.

Moreover, the conventional electric power system may not meet theconditions required for the continuous operation of the system in theevent of low voltage in the system.

SUMMARY

The present disclosure can prevent a generator from being separated fromthe power grid, by using a resistance device to detect and control anovercurrent induced above a rated current in the event of low voltage inthe power grid.

The present disclosure can also prevent a generator from being separatedfrom the power grid, by using a resistance device in a direct currentcapacitor of a power converting unit, which is connected to thegenerator, to detect and control an overvoltage induced above a ratedvoltage in the event of low voltage in the power grid.

Moreover, the present disclosure can provide a more reliable quality ofpower by implementing an efficient power generation system in which agenerator equipped with a power converting unit is well connected to thepower grid and maintained, regardless of the types of the generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the configuration of a power generation systemincluding a power control apparatus in accordance with an embodiment ofthe present disclosure;

FIG. 2 is a block diagram of a power control apparatus in accordancewith an embodiment of the present disclosure;

FIG. 3 is a flowchart illustrating a method of controlling power inaccordance with an embodiment of the present disclosure;

FIG. 4 illustrates the configuration of a power generation systemincluding a power control apparatus in accordance with anotherembodiment of the present disclosure;

FIG. 5 is a block diagram of a power control apparatus in accordancewith another embodiment of the present disclosure;

FIG. 6 is a flowchart illustrating a method of controlling power inaccordance with another embodiment of the present disclosure; and

FIGS. 7 and 8 illustrate a power control apparatus and a method ofcontrolling power in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Certain embodiments in accordance with the present disclosure will bedescribed in more detail through the below description with reference tothe accompanying drawings.

FIG. 1 illustrates the configuration of a power generation systemincluding a power control apparatus in accordance with an embodiment ofthe present disclosure, and FIG. 2 shows a block diagram of a powercontrol apparatus in accordance with an embodiment of the presentdisclosure.

Furthermore, FIGS. 7 and 8 illustrate a power control apparatus and amethod of controlling power in accordance with an embodiment of thepresent disclosure. Hereinafter, the following description will refer toFIGS. 7 and 8 when deemed necessary.

Referring to FIGS. 1 and 2, a power generation system in accordance withan aspect of the present disclosure includes a generator 10, a powerconverting unit 20, which is connected to the generator 10 and convertspower generated from the generator 10, and a power control apparatus 30,which controls overcurrents by using electric currents measured at thepower converting unit 20 and the generator 10.

Although it is preferred that the power generation system in accordancewith an aspect of the present disclosure is applied in a wind powergeneration system, it shall be evident to those of ordinary skill in theart that the present disclosure is not restricted to the wind powergeneration system and can be applied to any power generation systemusing natural powers.

More specifically, the generator 10 in accordance with an aspect of thepresent disclosure may be an electric power generating device forgenerating power. The generator 10 can be a squirrel cage inductiongenerator or a permanent magnet generator, and it shall be evident tothose of ordinary skill in the art that any generator that can be usedfor a generator can be applied to the present disclosure.

Next, the power converting unit 20 is a power converting device that isconnected to the generator 10 and can steadily supply power generated bythe generator 10.

The power converting unit 20 can include a converter (not illustrated),which converts an alternating current into a direct current, and aninverter (not illustrated), which converts a direct current into analternating current.

The power converting unit 20 can convert unstable power generated by thegenerator 10 into a constant output, by using the converter and theinverter, thereby producing more reliable quality of electric power.

Next, the power control apparatus 30 includes a current comparator 40,which is connected to a generator generating power and calculates anerror current by comparing a current measured at the generator and arated current of the generator, a controlling unit 50, which calculatesa real power value by receiving the error current and outputs a switchdriving signal corresponding to the calculated real power value, aswitch 60, which is operated by the switch driving signal of thecontrolling unit 50, and a resistance device 70, which is connected tothe switch 60 and consumes the error current.

The current comparator 40 calculates an error current (e_(I)), which isa difference in current, by comparing a current (I) measured at a rotorof the generator 10 and a rated current (I_(rated)) of the rotor. Here,the rated current (I_(rated)) is a current that is required for stablesupply of power, and can be predetermined by an operator.

The controlling unit 50 includes a controller 52, which performscontrolling by receiving the error current (e_(I)), and a driver 54,which controls the operation of a plurality of switches in accordancewith a real power (P), which is a control value of the controller 52.

The controller 52 can be one of a proportional (P) controller, aproportional derivative (PD) controller, a proportional integral (PI)controller and a proportional integral derivative (PID) controller, andcan perform linear control.

The driver 54 can control the operation of the plurality of switches byoutputting a driving signal to each of the plurality of switches inaccordance with a real power value calculated by the controller 52.

As illustrated in FIG. 4, the driver 54 can transfer an output signal ofthe driving signal that varies depending on the real power value.

The driver 54 can drive an n number of switches (n being a naturalnumber) that correspond to a calculated real power value selected frompre-determined table values.

As illustrated in FIG. 8, the table values are constituted by switchesbeing driven in accordance with the calculated real power value and theresistance value of resistance components connected to the switches. Inorder to consume overcurrents corresponding to the real power value, anappropriate n number of switches (n being a natural number) may beselected.

The switch 60 is operated by the switch driving signal of thecontrolling unit 50, and can guide an error current to the resistancedevice 70.

The switch 60 can be a plurality of power element switches, and it shallbe evident to those of ordinary skill in the art that a switch commonlyused for controlling power can be used for the switch 60. For example, athyristor can be used as the power element switch. In the followingdescription, the thyristor will be used as an example of the powerelement switch.

The resistance device 70 includes a resistance component that isconnected to the switch and consumes an error current in case the errorcurrent is distributed.

The resistance device 70 can include a plurality of resistancecomponents. Each of the plurality of resistance components can beconnected to each of the plurality of switches 60, respectively, andthus an error current can be consumed at a corresponding resistancecomponent in accordance with the operation of the switches 60. Here, theplurality of resistance components can have different resistance valuesfrom one another so as to select the switch 60 driven in accordance withthe real power value.

For example, in case the controller 52 is constituted by a proportionalintegral (PI) controller, the real power (P) can be calculated by thefollowing equation. Here, it shall be assumed that a proportional gainof the proportional integral controller is 3, an integral gain thereofis 2, and the time thereof is 0.2 seconds.P=3e _(I)+2∫₀ ^(0.2) e _(I)(t)dt  Mathematical Equation 1

Here, if it is assumed that the rated current (I_(rated)) is 1 ampereand the measured current (I) is 1.9 amperes, the error current (e_(I))can be 0.1 ampere. Applied to the above equation, the real power (P) canbe 0.26 watts.

Referring to FIG. 7, if it is assumed that PI=0.1 watt, P2=0.2 watts,P3=0.3 watts, . . . , and P10=1 watt, the real power (P) of 0.26 watts,which has been calculated earlier, can be positioned between P2 and P3,and thus the driver's output signal can become 2. Referring to FIG. 8,since the driver's output signal is 2, switch S1 is off, which shows astate of non-operation, and switch S2 is on, which shows a state ofoperation.

FIG. 3 is a flowchart illustrating a method of controlling power inaccordance with an embodiment of the present disclosure.

In step S310, with reference to FIG. 3, the power control apparatus 30measures a current of a rotor of the generator 10.

In step S320, the power control apparatus 30 calculates the errorcurrent (e_(I)) by using a difference between the measured current (I)and the rated current (I_(rated)) of the rotor of the generator 10.

In step S330, the power control apparatus 30 calculates a real power (P)that can control an overcurrent by using the calculated error current(e_(I)), which is the overcurrent that exceeds the rated current(I_(rated)).

In step S340, the power control apparatus 30 outputs a switch drivingsignal to a plurality of thyristors, depending on the calculated realpower (P) value.

In step S350, while the plurality of thyristors S₁, S₂, . . . , andS_(n) are driven by the switch driving signal, the error current (eI)passes through the switches, i.e., the thyristors S₁, S₂, . . . , andS_(n).

The operation of the switches will be described in more detail withreference to FIGS. 7 and 8. In the power control apparatus 30, if thereal power (P) value is P₃, the switch driving signal becomes 3. Then,if the switch driving signal is 3, the switches S₁ and S₂ are turned onand the remaining switches are turned off. Here, the switch to be drivenin accordance with the real power value can be selected in accordancewith a combination of the resistance values of resistance componentsthat are connected to the switches. This creates a set that can be savedas a table in the power control apparatus 30 (more specifically, in thedriver 54) and can be used.

Therefore, the power control apparatus 30 can efficiently consume anerror current by transferring a switch driving signal to an n number ofswitches (n) being a natural number) that are to be driven in accordancewith the real power value.

In step S360, the power control apparatus 30 consumes the error current(e_(I)) at a resistance component.

FIG. 4 illustrates the configuration of a power generation systemincluding a power control apparatus in accordance with anotherembodiment of the present disclosure, and FIG. 5 is a block diagram of apower control apparatus in accordance with another embodiment of thepresent disclosure.

Referring to FIGS. 4 and 5, a power generation system in accordance withanother embodiment of the present disclosure includes the generator 10,the power converting unit 20, which is connected to the generator 10 andconverts power generated by the generator 10, and a power controlapparatus 80, which controls overcurrents by using voltages measured ata direct current capacitor 25 of the power converting unit 20. Here, theovercurrent can be a current (I_(dc)) that is received from the directcurrent capacitor 25.

Below, no redundant description of the power generation system includingthe power control apparatus in accordance with an earlier embodiment ofthe present disclosure will be repeated.

The power converting unit 20 can include a converter (not illustrated),which converts an alternating current into a direct current, an inverter(not illustrated), which converts a direct current into an alternatingcurrent, and the direct current capacitor 25, which connects theconverter and the inverter with each other.

The power converting unit 20 can convert unstable power generated by thegenerator 10 into a constant output by using the converter and theinverter, thereby producing a more reliable quality of power.

Next, the power control apparatus 80 includes a voltage comparator 45,which calculates an error voltage by comparing a voltage measured at thedirect current capacitor 25 converting a direct current into analternating current and a rated current of the direct current capacitor25, the controlling unit 50, which calculates a real power value byreceiving the error voltage and outputs a switch driving signalcorresponding to the calculated real power value, the switch 60, whichis operated by the switch driving signal of the controlling unit 50, andthe resistance device 70, which is connected to the switch 60 andconsumes an error current corresponding to the error voltage. Here, theerror current corresponding to the error voltage can be an overcurrentthat exceeds the rated current and can be a current (I_(dc)) that isreceived from the direct current capacitor 25.

The voltage comparator 45 calculates an error voltage (e_(V)), which isa voltage difference, by comparing a measured voltage (V_(dc)), which ismeasured at the direct current capacitor 25, and a rated voltage(V_(dc,rated)) of the direct current capacitor 25. Here, the ratedvoltage (V_(dc,rated)) is a voltage for stable supply of power, and canbe predetermined by an operator.

The controlling unit 50 includes the controller 52, which performscontrolling by receiving the error voltage (e_(V)), and the driver 54,which controls the operation of a plurality of switches in accordancewith a real power (P), which is a control value of the controller 52.

The controller 52 can be one of a proportional (P) controller, aproportional derivative (PD) controller, a proportional integral (PI)controller and a proportional integral derivative (PID) controller, andcan perform linear control.

The driver 54 can control the operation of the plurality of switches byoutputting a driving signal to each of the plurality of switches inaccordance with a real power value calculated by the controller 52.

As illustrated in FIG. 7, the driver 54 can transfer an output signal ofthe driving signal that varies depending on the real power value.

The driver 54 can drive an n number of power element switches (n being anatural number) that correspond to a calculated real power valueselected from predetermined table values.

As illustrated in FIG. 8, the table values are constituted by powerelement switches being driven in accordance with the calculated realpower value and the resistance value of resistance components connectedto the switches. In order to consume overcurrents corresponding to thereal power value, an appropriate n number of switches (n being a naturalnumber) may be selected.

The switch 60 is operated by the switch driving signal of thecontrolling unit 50, and can guide an overcurrent corresponding to theerror voltage (e_(V)) to the resistance device 70.

The switch 60 can be a plurality of power element switches, and it shallbe evident to those of ordinary skill in the art that any switchcommonly used for controlling power can be used for the switch 60.

The resistance device 70 includes a resistance component that isconnected to the switch and consumes an error current in case anovercurrent corresponding to the error voltage (e_(V)) is distributed.

The resistance device 70 can include a plurality of resistancecomponents. Each of the plurality of resistance components can beconnected to each of the plurality of switches 60, respectively, andthus an error current corresponding to the error voltage (e_(V)) can beconsumed at a corresponding resistance component in accordance with theoperation of the switches 60. Here, the plurality of resistancecomponents can have different resistance values from one another, and aswitch 60 to be driven in accordance with the real power value can beselected.

For example, in case the controller 52 is constituted by a proportionalintegral (PI) controller, the real power (P) can be calculated by thefollowing equation. Here, it shall be assumed that a proportional gainof the proportional integral controller is 3, an integral gain thereofis 2, and the time thereof is 0.2 seconds.P=3e _(V)+2∫₀ ^(0.2) e _(V)(t)dt  Mathematical Equation 2

Here, if it is assumed that the rated voltage (V_(dc,rated)) is 1 voltand the measured voltage (V_(dc)) is 1.9 volts, the error voltage(e_(V)) can be 0.1 volt. Applied to the above equation, the real power(P) can be 0.26 watts

Referring to FIG. 7, if it is assumed that P1=0.1 watt, P2=0.2 watts,P3=0.3 watts, . . . , and P10=1 watt, the real power (P) of 0.26 watts,which has been calculated above, can be positioned between P2 and P3,and thus the driver's output signal can become 2. Referring to FIG. 8,since the driver's output signal is 2, switch S1 is off, which shows astate of non-operation, and switch S2 is on, which shows a state ofoperation.

FIG. 6 is a flowchart illustrating a method of controlling power inaccordance with another embodiment of the present disclosure.

In step S610, with reference to FIG. 6, the power control apparatus 80measures a voltage of the direct current capacitor 25 of the powerconverting unit 20.

In step S620, the power control apparatus 80 calculates the errorvoltage (e_(V)) by using a difference between the measured voltage(V_(dc)) measured at the direct current capacitor 25 and the ratedvoltage (V_(dc,rated)) of the direct current capacitor 25.

In step S630, the power control apparatus 80 calculates a real power (P)that can control an overcurrent corresponding to an overvoltage by usingthe calculated error voltage (e_(V)), which is the overvoltage thatexceeds the rated voltage (V_(dc,rated)).

In step S640, the power control apparatus 80 outputs a switch drivingsignal to a plurality of power element switches, depending on thecalculated real power (P) value.

In step S650, while the plurality of power element switches S₁, S₂, . .. , and S_(n) are driven by the switch driving signal, an error currentcorresponding to the error voltage (e_(V)) passes through the switches,i.e., the power element switches S₁, S₂, . . . , and S_(n). Here, theerror current is a current that exceeds the rated current.

The operation of the switches will be described in more detail withreference to FIGS. 7 and 8. In the power control apparatus 80, if thereal power (P) value is P3, the switch driving signal becomes 3. Then,if the switch driving signal is 3, switches S₁ and S₂ are turned on andthe remaining switches are turned off. Here, the switch to be driven inaccordance with the real power value can be selected in accordance witha combination of the resistance values of resistance components that areconnected to the switches. This creates a set that can be saved as atable in the power control apparatus 80 (more specifically, in thedriver 54) and can be used.

Therefore, the power control apparatus 80 can efficiently consume anerror current by transferring a switch driving signal to an n number ofswitches (n being a natural number) that are to be driven in accordancewith the real power value.

In step S660, the power control apparatus 80 consumes an error currentcorresponding to the error voltage (e_(V)) at a resistance component.

Certain embodiments of the present disclosure can include acomputer-readable medium that includes a program of instructions forexecuting operations that are realized in a variety of computers. Thecomputer-readable medium can include a program command, a local datafile or a local data structure, or a combination thereof. The recordedmedium can be designed and configured specifically for the presentdisclosure, or can be a medium that is disclosed to those of ordinaryskill in the computer software industry.

While the spirit of the present disclosure has been described in detailwith reference to particular embodiments, the embodiments are forillustrative purposes only and shall not limit the disclosure. It is tobe appreciated that those skilled in the art can change or modify theembodiments without departing from the scope and spirit of thedisclosure. As such, many embodiments other than those set forth abovecan be found in the appended claims.

1. A power control apparatus in a power generation system including agenerator generating power, the power control apparatus being connectedto a power converter to control power, the power converter including aconverter converting an alternating current into a direct current, aninverter converting a direct current into an alternating current and adirect current capacitor being connected to the converter and theinverter in parallel, the power control apparatus comprising: a voltagecomparator configured to calculate an error voltage, based on adifference between a voltage measured at the direct current capacitorand a rated voltage of the direct current capacitor; a controlling unitconfigured to calculate a real power value by receiving the errorvoltage and output an output switch driving signal corresponding to thecalculated real power value; a switch configured to be operated by theswitch driving signal; and a resistance device coupled to the switch toconsume an error current corresponding to the error voltage, wherein theerror current is a current being received from the direct currentcapacitor.
 2. The power control apparatus of claim 1, wherein thecontrolling unit comprises: a controller configured to calculate a realpower value by receiving the error voltage; and a driver configured tooutput a driving signal to each of a plurality of switches in accordancewith the calculated real power value.
 3. The power control apparatus ofclaim 1, wherein the switch is a power element switch.
 4. The powercontrol apparatus of claim 3, wherein there are an n number of powerelement switches, n being a natural number, and the number of the powerelement switches to be driven is adjusted according to the real powervalue.
 5. The power control apparatus of claim 1, wherein the resistancedevice comprises an m number of resistance elements, m being a naturalnumber, and the error current is consumed at the resistance elementconnected to the switch in accordance with the driving signal of theswitch.
 6. The power control apparatus of claim 1, wherein the powergeneration system is a wind power generation system.